Pneumatic sorting systems are employed in a variety of applications, including automated optical inspection and sorting equipments. Such pneumatic sorting systems for automated optical inspection and sorting equipment are described in U.S. application No. 07/890,967 of Datari for a "Hole Sorting System and Method" that is assigned to the assignee of this application.
FIG. 1 shows a prior art automatic inspection and sorting system 10 that is capable of inspecting and sorting, for example, raw or processed fruits or vegetables, wood chips, recycled plastics, and other similar articles.
In operation, a conveyor belt 12 carries articles 14 in a direction 16 through an inspection area 18 of a video camera 20. Video camera 20 delivers to a video signal processor 22 a video signal representing the optical characteristics of articles 14. Video signal processor 22 is programmed to identify particular characteristics of articles 14 such as, for example, color, shape, size, or the presence of defects. Articles 14 that include a defect 24 can thereby be separated from articles 14 that do not include a defect.
After articles 14 pass through inspection area 18, they are propelled along a trajectory 26 toward an acceptance conveyor belt 28 that carries acceptable articles to subsequent processing stations (not shown). Whenever video signal processor 22 determines from the video signal that an article 14 includes a defect 24, an ejection activation signal is delivered to a suitable one of multiple air ejection modules 30. In response to the ejection activation signal, the suitable ejection module 30 generates a blast of air 32 that deflects defective article 24 from trajectory 26 toward a reject chute 34. Typically, articles 24 are deflected into reject chute 34 where they are funneled toward a reject conveyor belt 36 for removal. Reject chute 34 is intended to reduce spillage of defective articles. However, a problem with prior art system 10 is that rapid sorting of large quantities of articles 24 typically requires frequent air blasts 32 that result in large quantities of compressed air flowing into the article sorting area. The resulting air flow is turbulent and can cause disruption of article flow along trajectory 26 and spillage of rejected articles that would otherwise be directed toward reject chute 34.
The problem is especially significant when sorting small, lightweight articles 24 such as plastic flakes, potato chips, or the like. The air turbulence tends to lift and carry such articles 24 out of defect chute 34 before they can fall onto reject conveyor belt 36.
Prior attempts at solving these problems include providing vents or exhausts by forming in reject chute 34 perforated metal screens or small punched louvers. The problem with such vents or exhausts is that small articles 24 tend to leak through the perforations or louvers, whereas larger articles 24 tend to block the perforations or louvers. In particular, U.S. Pat. No. 3,097,161 issued Jul. 9, 1963 for CAPSULE INSPECTION AND SEPARATION, U.S. Pat. No. 4,082,189 issued Apr. 4, 1978 for APPARATUS FOR SEPARATING FOOD ARTICLES FROM FIELD DEBRIS, and U.S. Pat. No. 4,191,294 issued Mar. 4, 1980 for an EMPTY CAPSULE EJECTOR all describe pneumatic sorting systems in which air is vented through screens, grids, or other similar structures.
Some prior pneumatic sorting systems employ active exhausts vented through generally open ducts. Such actively vented systems tend to draw defective articles away from the reject conveyor belt and into the exhaust system. In particular, U.S. Pat. No. 3,097,744 issued Jul. 16, 1963 for a QUALITATIVE PHOTOMETRIC MATERIALS SORTER, U.S. Pat. No. 3,179,247 issued Apr. 20, 1965 for a RANDOM STREAM MATERIALS SORTER, and U.S. Pat. No. 5,116,486 issued May 26, 1992 for an APPARATUS AND METHOD FOR SEPARATING RECYCLABLE WASTE all describe pneumatic sorting systems in which excess air is vented through a generally open duct.
Other prior active venting devices of types not used in sorting systems are described in U.S. Pat. No. 3,405,820 issued Oct. 15, 1968 for DUST PROOF HOPPER and U.S. Pat. No. 3,908,720 issued Sep. 30, 1975 for CONTROL OF DUST DURING DISCHARGE OF MATERIALS INTO HOPPERS. These patents describe hoppers with associated chambers through which dust is actively exhausted from materials discharged into the hoppers. In particular, U.S. Pat. No. 3,405,820 shows in FIG. 4 a duct between an outer shell 2 and an inner shell 3 having an inner-facing lower lip (unnumbered), and U.S. Pat. No. 3,908,720 shows in FIG. 2 how dust is exhausted through apertures 6 and 7 into an inclined chamber 5.
A prior passive venting device of a type not used in a sorting system is described in U.S. Pat. No. 4,969,494 issued Nov. 30, 1990 for a FILTERING DEVICE and shows a generally conical structure for removing dust from air or other gas. As shown in FIG. 1, the device includes successive inclined conical chambers through which the gas passes while allowing the dust or other particulates to fall away. The gas flows in a serpentine manner through each of the chambers along both sides of the defining baffle and is eventually vented through a screen 13.
What is needed, therefore, is a pneumatic sorting system that passively removes air from the sorting area in such a manner that small, lightweight articles can be properly sorted without disrupting the sorting trajectory or causing article spillage.